Semiconductor device and method of formation

ABSTRACT

A semiconductor device and method of formation are provided. The semiconductor device includes a substrate, a first active area over the substrate, a second active area over the substrate, a graphene channel between the first active area and the second active area, and a first in-plane gate. In some embodiments, the graphene channel, the first in-plane gate, the first active area, and the second active area include graphene. A method of forming the first in-plane gate, the first active area, the second active area, and the graphene channel from a single layer of graphene is also provided.

RELATED APPLICATION

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 15/852,391, titled “SEMICONDUCTOR DEVICE AND METHODOF FORMATION” and filed on Dec. 22, 2017, which is a divisional of andclaims priority to U.S. patent application Ser. No. 15/381,047, titled“SEMICONDUCTOR DEVICE AND METHOD OF FORMATION” and filed on Dec. 15,2016, which is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/455,992, titled “SEMICONDUCTOR DEVICE AND METHODOF FORMATION” and filed on Aug. 11, 2014. U.S. patent applications Ser.Nos. 15/852,391, 15/381,047 and 14/455,992 are incorporated herein byreference.

BACKGROUND

In a semiconductor device, such as a transistor, current flows through achannel region between a source region and a drain region uponapplication of a sufficient voltage or bias to a gate of the device.When current flows through the channel region, the transistor isgenerally regarded as being in an ‘on’ state, and when current is notflowing through the channel region, the transistor is generally regardedas being in an ‘off’ state.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is an illustration of a top down view of a semiconductor devicein accordance with some embodiments.

FIG. 2 is an illustration of a cross sectional view of a semiconductordevice in accordance with some embodiments.

FIG. 3 is an illustration of a top down view of a semiconductor devicein accordance with some embodiments.

FIG. 4 is an illustration of a cross sectional view of a semiconductordevice in accordance with some embodiments.

FIG. 5 is a flow diagram illustrating a method of making a semiconductordevice, in accordance with some embodiments.

FIG. 6 is an illustration of a cross sectional view of a semiconductordevice at a stage of fabrication, in accordance with some embodiments.

FIG. 7 is an illustration of a cross sectional view of a semiconductordevice at a stage of fabrication, in accordance with some embodiments.

FIG. 8 is an illustration of a cross sectional view of a semiconductordevice at a stage of fabrication, in accordance with some embodiments.

FIG. 9 is an illustration of a cross sectional view of a semiconductordevice at a stage of fabrication, in accordance with some embodiments.

FIG. 10 is an illustration of a cross sectional view of a semiconductordevice at a stage of fabrication, in accordance with some embodiments.

FIG. 11 is an illustration of a cross sectional view of a semiconductordevice at a stage of fabrication, in accordance with some embodiments.

FIG. 12 is an illustration of a cross sectional view of a semiconductordevice at a stage of fabrication, in accordance with some embodiments.

FIG. 13 is an illustration of a top down view of a semiconductor deviceat a stage of fabrication, in accordance with some embodiments.

FIG. 14 is a flow diagram illustrating a method of making asemiconductor device, in accordance with some embodiments.

FIG. 15 is a flow diagram illustrating a method of making asemiconductor device, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

One or more techniques for forming a semiconductor device and resultingstructures formed thereby are provided herein. Some embodiments of thepresent disclosure have one or a combination of the following featuresand/or advantages.

According to some embodiments, a semiconductor device comprises agraphene channel between a first active area and a second active area.In some embodiments, the graphene channel comprises a first sideproximate a first in-plane gate and a second side proximate a secondin-plane gate. In some embodiments, at least one of the first in-planegate or the second in-plane gate comprises at least one of nickel,copper, gold, etc. In yet another embodiment, at least one of the firstin-plane gate, the second in-plane gate, the first active area, or thesecond active area comprises graphene. In some embodiments, by formingat least one of the first in-plane gate, the second in-plane gate, thefirst active area, or the second active area from graphene, a heightdifference between the graphene channel and at least one of the firstin-plane gate, the second in-plane gate, the first active area, or thesecond active area is reduced. In some embodiments, replacing at leastone of the first in-plane gate, the second in-plane gate, the firstactive area, or the second active area with graphene simplifies thefabrication process for the semiconductor device.

FIGS. 1 and 3 are top down views of the semiconductor device 100, andFIGS. 2 and 4 are cross-sectional views of the semiconductor device 100,according to some embodiments. Turning to FIGS. 1 and 2, where FIG. 2illustrates a cross section of the semiconductor device 100 taken alongline 1-1 in FIG. 1, according to some embodiments. In some embodiments,a dielectric layer 104 is formed over a substrate 102, as illustrated inFIG. 2. In some embodiments, the substrate 102 comprises at least one ofsilicon, germanium, carbon, etc. In some embodiments, the substrate 102comprises silicon. In some embodiments, the substrate 102 includes atleast one of an epitaxial layer, a silicon-on-insulator (SOI) structure,a wafer, or a die formed from a wafer. In some embodiments, thesubstrate 102 has a first thickness 130. In some embodiments, the firstthickness 130 is between about 350 micrometers to about 525 micrometers.In some embodiments, the dielectric layer 104 comprises at least one ofan oxide, a nitride, etc. In some embodiments, the dielectric layer 104comprises a silicon oxide, such as SiO₂. In some embodiments, thedielectric layer 104 includes at least one of an epitaxial layer, asilicon-on-insulator (SOI) structure, a wafer, or a die formed from awafer. In some embodiments, the dielectric layer 104 has a secondthickness 132. In some embodiments, the second thickness 132 is betweenabout 10 nanometers to about 300 nanometers.

In some embodiments, the semiconductor device 100 comprises a firstactive area 106 and a second active area 108. In some embodiments, atleast one of the first active area 106 or the second active area 108comprises at least one of a source or a drain. In some embodiments, thefirst active area 106 comprises at least one of a first conductivitytype or a second conductivity type. In some embodiments, the secondactive area 108 comprises at least one of the first conductivity type orthe second conductivity type. In some embodiments, the firstconductivity type comprises at least one of n-type or p-type. In someembodiments, the first conductivity type comprises n-type when thesecond conductivity type comprises p-type and the second conductivitytype comprises n-type when the first conductivity type comprises p-type.In some embodiments, at least one of the first active area 106 or thesecond active area 108 has a third thickness 134. In some embodiments,the third thickness 134 is between about 50 nanometers to about 100nanometers.

In some embodiments, a graphene channel 110 is formed over the substrate102. In some embodiments, the graphene channel 110 is formed over thedielectric layer 104. In some embodiments, the graphene channel 110comprises graphene. In some embodiments, the graphene channel 110comprises about 70% graphene to about 90% graphene. In some embodiments,the graphene channel 110 is between the first active area 106 and thesecond active area 108. In some embodiments, the graphene channel 110has a first side 111 and a second side 114. In some embodiments, thegraphene channel 110 has a channel length 136, as illustrated in FIG. 1.In some embodiments, the channel length 136 is between about 5micrometer to about 75 micrometers. In some embodiments, the channellength 136 is between about 25 micrometers to about 35 micrometers. Insome embodiments, the graphene channel 110 has a channel width 138, asillustrated in FIG. 2. In some embodiments, the channel width 138 isbetween about 1 micrometer to about 25 micrometers. In some embodiments,the channel width 138 is between about 5 micrometers to about 15micrometers. In some embodiments, the graphene channel 110 has a channelheight 140. In some embodiments, the channel height 140 is between about1 angstrom to about 500 angstroms.

In some embodiments, the semiconductor device 100 comprises at least oneof a first in-plane gate 116 or a second in-plane gate 118. In someembodiments, at least one of the in-plane gates 116-118 is located inthe same plane or layer as an electrode for which it performs a gatingfunction, such as applying a bias. In some embodiments, at least one ofthe in-plane gates 116-118 applies at least one of a first bias or asecond bias to the semiconductor device 100. In some embodiments, atleast one of the in-plane gates 116-118 is in the same plane as at leastone of the graphene channel 110, the first active area 106, or thesecond active area 108. In some embodiments, at least one of thein-plane gates 116-118 is proximate at least one of the first side 111or the second side 114 of the graphene channel 110. In some embodiments,the first in-plane gate 116 is proximate the first side 111 of thegraphene channel 110 and the second in-plane gate 118 is proximate thesecond side 114 of the graphene channel 110. In some embodiments, thefirst in-plane gate 116 is connected to the second in-plane gate 118. Insome embodiments, at least one of the in-plane gates 116-118 comprisesat least one of nickel, copper, graphene, gold, etc. In someembodiments, the utilization of at least one of the in-plane gates116-118 improves the electron mobility of the semiconductor device 100by positioning at least one of the in-plane gates 116-118 in the sameplane as at least one of the graphene channel 110, the first active area106, or the second active area 108. In some embodiments, at least one ofthe in-plane gates 116-118 is used to modulate a Fermi level of thegraphene channel 110. In some embodiments, a bottom gate 112 modulateddrain current characteristics will yield different doping result byapplying the in-plane gates 116-118.

In some embodiments, the semiconductor device 100 comprises a bottomgate 112, as illustrated in FIG. 2. In some embodiments, the bottom gate112 is located under the substrate 102. In some embodiments, the bottomgate 112 applies a third bias to the semiconductor device 100. In someembodiments, the bottom gate comprises at least one of nickel, copper,gold, etc.

Turning to FIGS. 3 and 4, where FIG. 4 illustrates a cross section ofthe semiconductor device 100 taken along line 3-3 in FIG. 3, accordingto some embodiments. In some embodiments, at least one of the firstin-plane gate 116, the second in-plane gate 118, the first active area106, the second active area 108 or the graphene channel 110 comprisesgraphene. In some embodiments, at least one of the first in-plane gate116, the second in-plane gate 118, the first active area 106, the secondactive area 108 or the graphene channel 110 is formed from a graphenelayer. In some embodiments, at least one of the first in-plane gate 116,the second in-plane gate 118, the first active area 106, the secondactive area 108 or the graphene channel 110 is formed by etching thegraphene layer. In some embodiments, at least one of the first in-planegate 116, the second in-plane gate 118, the first active area 106, thesecond active area 108, or the graphene channel 110 is formed from afirst layer of graphene stacked over a second layer of graphene (notshown). In some embodiments, at least one of the first in-plane gate116, the second in-plane gate 118, the first active area 106, or thesecond active area 108 has a fourth thickness 402. In some embodiments,the fourth thickness 402 is between about 1 angstrom to about 500angstroms. In some embodiments, the fourth thickness 402 issubstantially the same as the channel height 140. In some embodiments,forming at least one of the first in-plane gate 116, the second in-planegate 118, the first active area 106, or the second active area 108 froma single graphene layer reduces a height difference between the graphenechannel 110 and at least one of the first in-plane gate 116, the secondin-plane gate 118, the first active area 106, or the second active area108. In some embodiments, forming at least one of the first in-planegate 116, the second in-plane gate 118, the first active area 106, orthe second active area 108 from the same graphene layer simplifies thefabrication process for the semiconductor device 100.

Turing to FIG. 5, a method 500 of forming the semiconductor device 100is provided, according to some embodiments. At 502, a dielectric layer104 is formed over a substrate 102, as illustrated in FIG. 6. In someembodiments, at least one of the substrate 102 or the dielectric layer104 comprises at least one of silicon or silicon oxide. At 504, a carbonlayer 520 is formed, such as by deposition, over the dielectric layer104, as illustrated in FIG. 7. In some embodiments, the carbon layer 520is an amorphous carbon layer. In some embodiments, the carbon layer 520is deposited by a sputtering process. In some embodiments, thesputtering process comprises a radio frequency (RF) sputtering process.In some embodiments, the carbon layer 520 is deposited with a plasmapower of about 50 watts to about 150 watts for about 5 minutes to about20 minutes. In some embodiments, the carbon layer 520 is deposited for11 minutes with the plasma power of 90 watts. In some embodiments, thecarbon layer 520 has a fifth thickness 524. In some embodiments, thefifth thickness 524 is between about 10 nanometers to about 500nanometers.

At 506, a metal layer 522 is formed, such as by deposition, asillustrated by FIG. 8. In some embodiments, the metal layer 522comprises at least one of nickel, copper, etc. In some embodiments, themetal layer 522 has a sixth thickness 526. In some embodiments, thesixth thickness 526 is between about 50 nanometers to about 500nanometers. In some embodiments, the metal layer 522 is deposited with aplasma power of between about 20 to about 80 watts. In some embodiments,the metal layer 522 is deposited on the carbon layer 520 where grapheneis to be formed. At 508, an annealing process 530 is performed, asillustrated in FIG. 9. In some embodiments, the annealing process 530 isperformed at a temperature of between about 750° C. to about 1200° C. Insome embodiments, the annealing process 530 is performed for about 10minutes to about 20 minutes. In some embodiments, a second annealingprocess is performed. In some embodiments, during the annealing process,the carbon layer 520 is transformed into at least one of graphene layers532-534. In some embodiments, a first graphene layer 532 is formed on abottom surface 536 of the metal layer 522 and a second graphene layer534 is formed on a top surface 538 of the metal layer 522, asillustrated in FIG. 10. In some embodiments, the first graphene layer532 has a seventh thickness 540. In some embodiments, the secondgraphene layer 534 has an eighth thickness 542. In some embodiments, atleast one of the seventh thickness 540 or the eighth thickness 542 isbetween about 1 angstrom to about 500 angstroms.

At 510, at least one of the metal layer 522 or the second graphene layer534 is removed, as illustrated in FIG. 11. In some embodiments, themetal layer 522 is removed by treating the metal layer 522 with an acidsolution. In some embodiments, the acid solution comprises about 10%hydrochloric acid. In some embodiments, the second graphene layer 534 onthe top surface 538 of the metal layer 522 is removed by an oxygenplasma process. In some embodiments, the second graphene layer 534 isdeposited on the first graphene layer 532 after the metal layer 528 hasbeen removed, as illustrated in FIG. 12. In some embodiments, the secondgraphene layer 534 is discarded. At 512, at least one of a first activearea 106, a second active area 108, a first in-plane gate 116, a secondin-plane gate 118, or a graphene channel 110 is formed. In someembodiments, at least one of the graphene layers 532-534 are etched todefine at least one of the first active area 106, the second active area108, the first in-plane gate 116, the second in-plane gate 118, or thegraphene channel 110, as illustrated by the top down view of thesemiconductor device 100 of FIG. 13.

Turing to FIG. 14, a method 1400 of forming the semiconductor device 100is provided, according to some embodiments. At 1402, a carbon layer 520is formed, such as by deposition, over at least one of a substrate 102or a dielectric layer 104. In some embodiments, the carbon layer 520 isan amorphous carbon layer. At 1404, a pattern is formed on the carbonlayer 520. In some embodiments, the pattern is formed by aphotolithography process. In some embodiments, the pattern is defined bya photoresist. At 1406, a metal layer 522 is deposited over the pattern.In some embodiments, the metal layer 522 is deposited by a sputteringprocess. In some embodiments, the metal layer 522 comprises at least oneof copper, nickel, gold, etc.

At 1408, a lift off process is performed on the metal layer 522. In someembodiments, the photoresist under the metal layer 522 is removed, aswell as the metal layer 522 under the photoresist. In some embodiments,the photoresist is removed with a solvent. In some embodiments, thesolvent is at least one of hydrochloric acid or ferric nitrate. At 1410,at least one of a first graphene layer 532 or second graphene layer 534is formed. In some embodiments, at least one of the first graphene layer532 or the second graphene layer 534 is formed by an annealing process.In some embodiments, the annealing process is performed at a temperatureof between about 750° C. to about 1200° C. In some embodiments, theannealing process is performed for about 10 minutes to about 20 minutes.In some embodiments, the first graphene layer 532 is between thedielectric layer 104 and the metal layer 522. In some embodiments, atleast one of the first graphene layer 532 or the second graphene layer534 is produced by at least one of segregation or precipitation of acarbon species from the carbon layer 520. At 1412, at least one of thesecond graphene layer 534 or the metal layer 522 is removed. In someembodiments, the metal layer 522 is removed by at least one of anetching process or by submersion in a solvent, such as hydrochloric acidor ferric nitrate. In some embodiments, the second graphene layer 534 isremoved by an oxygen plasma process. At 1414, at least one of a firstactive area 106, a second active area 108, a first in-plane gate 116, asecond in-plane gate 118, or a graphene channel 110 is formed.

Turning to FIG. 15, a method 1500 of forming a semiconductor device 100is provided, according to some embodiments. At 1502, a metal layer 522is formed, such as by deposition, over at least one of a substrate 102or dielectric layer 104. In some embodiments, the metal layer 522 isdeposited by a sputtering process. In some embodiments, the metal layer522 is deposited in a pattern or over a template. In some embodiments,the metal layer 522 comprises at least one of copper, nickel, gold, etc.In some embodiments, the metal layer 522 is about 300 nanometers thick.At 1504, a carbon source is provided. In some embodiments, the carbonsource comprises at least one of methane, ethane, propane, butane, etc.In some embodiments, the carbon source comprises dissociated carbonatoms, such as from methane, ethane, propane, butane, etc. In someembodiments, the carbon source is dissociated on the metal layer 522. At1506, at least one of a first graphene layer 532 or a second graphenelayer 534 is formed. In some embodiments, at least one of the graphenelayers 532-534 are formed by at least one of a chemical vapor deposition(CVD) process or molecular beam epitaxy (MBE) process. In someembodiments, at least one of the graphene layers 532-534 are formed byplacing the semiconductor device 100 in an oven with a gas mixture. Insome embodiments, the gas mixture comprises a mixture of at least one ofmethane, ethane, propane, nitrogen, hydrogen, etc. In some embodiments,the semiconductor device 100 is placed in the oven for about 2 minutesto about 15 minutes. In some embodiments, the oven is maintained at atemperature of about 850° C. to about 1200° C. In some embodiments, theoven is maintained at a temperature of about 900° C.

At 1508, at least one of second graphene layer 534 or the metal layer522 is removed. In some embodiments, second graphene layer 534 isremoved by an oxygen plasma process. In some embodiments, the metallayer 522 is removed by an etching process. In some embodiments, theetching process utilizes a wet etchant, such as ferric nitrate,hydrochloric acid, phosphoric acid, etc. In some embodiments, the secondgraphene layer 534 is deposited on the first graphene layer 532. At1510, at least one of a first active area 106, a second active area 108,a first in-plane gate 116, a second in-plane gate 118, or a graphenechannel 110 is formed. In some embodiments, at least one of the firstactive area 106, the second active area 108, the first in-plane gate116, the second in-plane gate 118 or the graphene channel 110 is formedfrom at least one of the graphene layers 532-534. In some embodiments,at least one of the first active area 106, the second active area 108,the first in-plane gate 116, or the second in-plane gate 118 is formedfrom at least one of gold, copper, nickel, etc.

According to some embodiments, a semiconductor device comprises asubstrate, a first active area over the substrate, a second active areaover the substrate, a graphene channel between the first active area andthe second active area, and a first in-plane gate. In some embodiments,the graphene channel has a first side and a second side. In someembodiments, the first in-plane gate is proximate the first side of thegraphene channel.

According to some embodiments, a semiconductor device comprises asubstrate, a first active area over the substrate, a second active areaover the substrate, a graphene channel between the first active area andthe second active area, and a first in-plane gate. In some embodiments,the graphene channel has a first side and a second side. In someembodiments, the first in-plane gate is proximate the first side of thegraphene channel. In some embodiments, the first in-plane gate comprisesgraphene.

According to some embodiments, a semiconductor device comprises asubstrate, a first active area over the substrate, a second active areaover the substrate, a graphene channel between the first active area andthe second active area, a first in-plane gate and a second in-planegate. In some embodiments, the graphene channel has a first side and asecond side. In some embodiments, the first in-plane gate is proximatethe first side of the graphene channel and the second in-plane gate isproximate the second side of the graphene channel. In some embodiments,the first in-plane gate and the second in-plane gate comprise graphene.

The foregoing outlines features of several embodiments so that those ofordinary skill in the art may better understand various aspects of thepresent disclosure. Those of ordinary skill in the art should appreciatethat they may readily use the present disclosure as a basis fordesigning or modifying other processes and structures for carrying outthe same purposes and/or achieving the same advantages of variousembodiments introduced herein. Those of ordinary skill in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the present disclosure, and that they may makevarious changes, substitutions, and alterations herein without departingfrom the spirit and scope of the present disclosure.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter of the appended claims is not necessarily limited tothe specific features or acts described above. Rather, the specificfeatures and acts described above are disclosed as example forms ofimplementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated having the benefitof this description. Further, it will be understood that not alloperations are necessarily present in each embodiment provided herein.Also, it will be understood that not all operations are necessary insome embodiments.

It will be appreciated that layers, features, elements, etc. depictedherein are illustrated with particular dimensions relative to oneanother, such as structural dimensions or orientations, for example, forpurposes of simplicity and ease of understanding and that actualdimensions of the same differ substantially from that illustratedherein, in some embodiments. Additionally, a variety of techniques existfor forming the layers, regions, features, elements, etc. mentionedherein, such as at least one of etching techniques, planarizationtechniques, implanting techniques, doping techniques, spin-ontechniques, sputtering techniques, growth techniques, or depositiontechniques such as chemical vapor deposition (CVD), for example.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication and the appended claims are generally be construed to mean“one or more” unless specified otherwise or clear from context to bedirected to a singular form. Also, at least one of A and B and/or thelike generally means A or B or both A and B. Furthermore, to the extentthat “includes”, “having”, “has”, “with”, or variants thereof are used,such terms are intended to be inclusive in a manner similar to the term“comprising”. Also, unless specified otherwise, “first,” “second,” orthe like are not intended to imply a temporal aspect, a spatial aspect,an ordering, etc. Rather, such terms are merely used as identifiers,names, etc. for features, elements, items, etc. For example, a firstelement and a second element generally correspond to element A andelement B or two different or two identical elements or the sameelement.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others of ordinary skill in the art based upon a readingand understanding of this specification and the annexed drawings. Thedisclosure comprises all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method of forming a semiconductor device,comprising: forming a dielectric layer over a first surface of asubstrate; forming a carbon layer over the dielectric layer; forming ametal layer over the carbon layer; performing an anneal process, whereinat least some of the carbon layer is transformed into graphene duringthe anneal process; removing the metal layer after performing the annealprocess; etching the graphene to define a channel and a source/drainregion from the graphene; and forming a first gate over a second surfaceof the substrate opposite the first surface.
 2. The method of claim 1,wherein the etching comprises etching the graphene to further define asecond gate from the graphene, the second gate spaced apart from thechannel.
 3. The method of claim 1, comprising: forming a second gateextending around the source/drain region from a first side of thechannel to a second side of the channel opposite the first side.
 4. Themethod of claim 1, wherein the carbon layer is an amorphous carbonlayer.
 5. The method of claim 1, wherein the metal layer comprises atleast one of nickel or copper.
 6. The method of claim 1, wherein theremoving comprises removing the metal layer using an acid solution. 7.The method of claim 1, wherein the removing comprises removing the metallayer using an oxygen plasma process.
 8. The method of claim 1,comprising: forming a metal gate adjacent the channel, wherein the metalgate extends around the source/drain region from a first side of thechannel to a second side of the channel opposite the first side.
 9. Themethod of claim 1, comprising: forming a metal gate adjacent thechannel, wherein the metal gate has a first thickness and the channelhas a second thickness less than the first thickness.
 10. A method offorming a semiconductor device, comprising: forming a carbon layer;patterning the carbon layer to define a patterned carbon layer; forminga metal layer over the patterned carbon layer; performing an annealprocess, wherein at least some of the patterned carbon layer istransformed into graphene during the anneal process to form a channelfrom the patterned carbon layer; forming a source/drain region; andforming a metal gate adjacent the channel, wherein the metal gateextends around the source/drain region from a first side of the channelto a second side of the channel opposite the first side.
 11. The methodof claim 10, wherein at least some of the patterned carbon layer istransformed into graphene during the anneal process to further form thesource/drain region from the patterned carbon layer.
 12. The method ofclaim 10, wherein the source/drain region is formed from the patternedcarbon layer.
 13. The method of claim 10, comprising: forming adielectric layer over a first surface of a substrate; and forming a gateover a second surface of the substrate opposite the first surface. 14.The method of claim 13, wherein the forming a carbon layer comprisesforming the carbon layer over the dielectric layer.
 15. A method offorming a semiconductor device, comprising: forming a carbon layer;performing an anneal process, wherein at least some of the carbon layeris transformed into graphene during the anneal process; etching thegraphene to define a channel and a source/drain region from thegraphene; and forming a first gate around the channel and thesource/drain region.
 16. The method of claim 15, wherein the forming afirst gate comprises forming the first gate to extend around thesource/drain region from a first side of the channel to a second side ofthe channel opposite the first side.
 17. The method of claim 15,comprising: forming a second gate under the channel.
 18. The method ofclaim 15, wherein: forming the carbon layer comprises forming the carbonlayer over a substrate, and the method comprises forming a second gateunder the substrate.
 19. The method of claim 18, comprising: forming adielectric layer over the substrate before forming the carbon layer,wherein the forming a carbon layer comprises forming the carbon layerover the dielectric layer.
 20. The method of claim 15, wherein theforming a first gate comprises forming the first gate from the graphene.